The application of metal coatings to various surfaces by means of thermally sprayed molten metal particle is well known in the art. In our above referenced patent application, we disclosed the application of anti-fouling coatings using this thermal spraying technique to marine structures, particularly hulls of boats and ships, but the process is also applicable generally to such exemplary structures as underwater pilings, power plant intake ducts, underwater energy conversion systems, buoys and the like where the fouling by marine growth interferes with or impedes the efficient operation of such apparatus.
As set forth in our application Ser. No. 481,412 entitled, "METHOD AND MEANS OF APPLYING ANTI-FOULING ON MARINE HULLS", various systems have been devised for applying anti-fouling substances, typically copper and copper alloys, to marine surfaces such as copper foils or in the form of panels or tiles which are adhered to hull surfaces. The most modern of these are paint and coating technologies depend on uniform consumption of the binder and toxin and biocide and therefore are limited by the thickness or number of coatings applied. In the tile or foil methods, painstaking tailoring of individual panels or tiles to the complete hull surfaces has, in general, not been found acceptable by the marine trades. In our above-identified application, we disclose a method of providing marine surfaces with anti-fouling metal layers such as metallic copper/copper nickel which are thermally sprayed or deposited on a previously applied coat of resinous material. The anti-fouling system included a resin layer which could be a polyurethane a polyester or epoxy resin which served two main functions: (1) provides an adhesive between the hull and a spray deposited copper or copper coating and (2) a seal layer to seal fine cracks in the gel coat of a fiberglass hull, for example, and (3) to prevent osmosis and a dielectric layer in the case of a steel hull to prevent electrolytic corrosion effects. The present invention provides a distinct improvement over the process disclosed in that application. This application includes incorporating hollow glass or ceramic spheres in the micronsize range (marketed under various trademarks such as Microballoons.TM., Microspheres.TM.) or the deposition of a foamed resin surface onto the resin layer which can be an air, heat or UV cured resin. This layer serves as the sealing and holding the firmly thermally sprayed anti-fouling coating. The mechanism is relatively simple in that the heavily filled layer is abraded by sanding or grit blasting sufficient to rupture, sheer and/or fracture the embedded micronspheres, microballoons or foamed voids. After the abrading process is completed, the surface is vacuumed or washed clean to remove the abraided material so that the surface now represents a porous surface with large numbers of undercuts, nooks and crannies. The sprayed molten copper now becomes embedded into these pores and in this manner, the bond strength is mechanically fixed. In the original application, the simple grit blasting provided adhesion of a thin layer of copper but if the heavier layer was desposited by the addition of multiple layers, the shrinkage of the copper could possibly cause sufficient stress to overcome the bond strength.